cxl: Free virtual PHB when removing

When adding a vPHB in cxl_pci_vphb_add(), we allocate a pci_controller
struct using pcibios_alloc_controller(). However, we don't free it in
cxl_pci_vphb_remove(), causing a leak.

Call pcibios_free_controller() in cxl_pci_vphb_remove() to free the vPHB
data structure correctly.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>